Brine treatment scaling control system and method

ABSTRACT

The present invention may be used in systems and methods for brine treatment scaling control in a water treatment system. A concentrated brine stream influent may be treated in an electrodialysis-reversal process to produce a concentrated brine stream effluent and a lower salinity diluent water, which may be potable water effluent. The concentrated brine stream effluent may be processed in a brine treatment scaling control system that may have a mixing vessel and a membrane filter with the mixing vessel seeded with calcium sulfate. A lowered salinity brine stream effluent may be produced for return to the electrodialysis-reversal process to allow operation at greater overall recovery and an elevated concentrated brine stream may be produced.

BACKGROUND OF THE INVENTION

This invention relates to systems and processes for controlling scalingmaterial in brine treatment systems that may be used to produce potablewater, recycled water, processed water and the like. Conversion ofbrackish and saline water may include a primary treatment using areverse osmosis or electrodialysis-reversal system and the concentratebrine stream produced may be further treated in anelectrodialysis-reversal system to increase potable and other type waterproduction and further concentrate the brine stream produced. The newsystem and method treats the concentrated brine stream loop tocontinuously remove calcium sulfate to reduce the scaling properties ofthe concentrated brine stream and to allow for higher treatment systemrecoveries.

Current brackish and saline water treatment systems and methods may usea primary process such as reverse osmosis (RO) orelectrodialysis-reversal (EDR) process with a secondary process such asan EDR process to treat a brine stream produced by the primary process.The resultant further concentrated brine stream may be disposed orwasted, or further treated with a zero liquid discharge process. A majorlimitation of water recovery for the secondary process for the brinestream may be the fouling of the secondary system due to scaling of theEDR membranes due to elevated levels of sparingly soluble salts, such ascalcium sulfate, in the brine stream. Current methods to control scalingmay include brine stream pre-treatment with chemicals that may be toxicor may include limiting the recovery. Calcium sulfate may be found inthe brine stream when sulfuric acid has been used for scale control.

SUMMARY OF THE INVENTION

The present invention is directed to systems and methods for brinetreatment scaling control in a water treatment system. A concentratedbrine stream influent may be treated in an electrodialysis-reversalprocess to produce a more concentrated brine stream effluent and lowersalinity diluent water, which may be potable water effluent. The moreconcentrated brine stream effluent may be processed in a brine treatmentscaling control system that may have a mixing vessel and a membranefilter with the mixing vessel seeded with calcium sulfate. A loweredsalinity brine stream effluent may be produced for return to the brineloop of the EDR process and an elevated concentrated brine stream may beproduced.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdrawings, description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a functional diagram of a brine treatment scalingcontrol system in combination with an EDR brine stream secondarytreatment system according to an embodiment of the invention;

FIG. 2 illustrates a functional diagram of a brine treatment scalingcontrol system in combination with an EDR brine stream secondarytreatment system according to an embodiment of the invention;

FIG. 3 illustrates a perspective schematic scaling control tubularmembrane reverse osmosis process according to an embodiment of theinvention.

DETAILED DESCRIPTION

The following detailed description represents the best currentlycontemplated modes for carrying out the invention. The description isnot to be taken in a limiting sense, but is made merely for the purposeof illustrating the general principles of the invention.

Referring to FIG. 1, an EDR process 10 may receive an influent stream 12influent which may be a concentrated brine stream, treated wastewater,groundwater, surface water, processed water and the like and may producea potable water 14 effluent and a concentrated brine stream 16 effluent.The concentrated brine stream 16 effluent may be processed in a brinetreatment scaling control system 20 that has a mixing vessel 30 and amembrane filter 24, that may be tubular, spiral, flat sheet or othersimilar filter that may accommodate a seed slurry feed. The brinetreatment scaling control system 20 may return a lowered salinity brinestream 26 as make-up flow to the brine loop of the EDR process 10concentrate circulating loop for further treatment.

The EDR process may transfer ions through membranes from a lessconcentrated solution to a more concentrated solution as a result of aflow of direct electric current. In an ionic solution in which twoelectrodes are immersed spaced apart, ions may begin to move toward eachelectrode when a direct current (DC) potential is applied to theelectrodes. Positively charged ions (cations) may migrate toward thecathode, or negatively charged electrode, and negatively charged ions(anions) may migrate toward the anode, or positively charged electrode.In an EDR system several membranes may be positioned in the spacebetween the electrodes to create water-tight compartments. Two types ofmembranes may be used; the generally identified anion transfer membranesthat allow the passage of negatively charged anions, and the cationtransfer membranes that allow the passage of positively charged cations.The two membrane types are placed between the electrodes in pairs andare impervious to water transfer.

The presence of the anion and cation membrane pairs may result in watercompartments that alternately become either depleted or concentratedwith ions when the direct current potential is applied. When the EDRsystem is properly manifolded, the membrane pairs will produce twoseparate flow streams, one that may be demineralized and one that may bemore concentrated with minerals. In a typical application, severalhundred combinations of demineralizing and concentrating compartmentsmay be assembled in a membrane stack. The membranes may be separated bymembrane spacers that allow space for water to flow across the membranesurfaces. A membrane stack may contain more than one pair of electrodes.The EDR system may be structured to allow the reversal of the directcurrent potential. The reversal may be done periodically to cause ionsto migrate alternatively in opposite directions such that a compartmentthat was a demineralizing compartment may become a concentratingcompartment and vice versa.

There may be two water process flow connections to a membrane stack. Oneconnection may allow water to flow through the demineralizationcompartment of the membrane stack and the other connection may allowwater to flow through the concentrating compartments of the membranestack. The latter may be termed the brine stream concentrate loop orbrine loop. There may also be connections to the electrode compartmentsisolated from the water treatment flow for flushing the electrodecompartments.

The flow rate of the concentrate and demineralized water through the EDRmembrane stack should be essentially equal. In order to save water andincrease the recovery of the EDR system, most of the concentrate brinestream may be recycled via the brine loop in an amount that wouldprevent the least soluble mineral from precipitating avoiding scaleformation on the membranes and in the brine loop. Discharging an amountof the brine stream concentrate to waste, and adding an equal amount offeed water to maintain the overall stream volume, controls theconcentration level in the concentrate brine stream and the brine loop.Acid and/or other anti-scalent chemicals may usually be fed continuouslyto the circulating concentrate brine stream to reduce the potential formineral scaling.

As the feed influent salinity to an EDR process increases, which may bethe case when an EDR process is used as a secondary treatment step, theconcentration of salts, and therefore the potential for scale formationin the brine stream concentrate loop increases. This condition may limitthe recovery levels in an EDR process when used in a secondary treatmentconfiguration.

As illustrated in FIG. 1 an EDR process 10 receives a concentrated brinestream 12 influent from a primary saline treatment system (not shown)and outputs a potable water 14 effluent and a concentrated brine stream16 effluent from the brine loop. The concentrated brine stream 16effluent may be filtered in a membrane filter 24, tubular, flat sheet orother similar filter that may accommodate seed slurry feed to output alowered salinity brine stream 26 that may be returned to the brine loopof the EDR process 10 as recycled influent for further treatment. Thetubular membrane filter 24 may also output an elevated concentratedbrine stream 28 as compared to the lowered salinity brine stream 26.

The concentrated brine stream 28 effluent of the tubular membrane filter24 may be mixed in a mixing vessel 30 that may contain calcium sulfate,gypsum crystals or other sparingly soluble salt crystals. The mixturemay have a portion returned to the tubular membrane filter 24, a portionremoved to maintain the materials balance in the seeded slurry processof the brine treatment system 20, and solids may be removed.

Another configuration of the brine treatment system 20 is illustrated inFIG. 2. In this configuration, the concentrate brine stream 16 effluentfrom the brine loop of the EDR process 10 may be routed to the mixingvessel 30 of the seeded slurry process that may contain the calciumsulfate or gypsum crystals. The mixture produced may then be pumped tothe membrane filter 24, tubular, flat sheet or other similar filter thatmay accommodate seed slurry feed. The lowered salinity brine stream 26effluent product may then be returned to the brine loop of the EDRprocess 10 as recycled influent to allow continued operation of the EDRprocess at higher recovery and efficiency. The tubular membrane filter24 may have membranes of the nanofiltration or reverse osmosis type. Theelevated concentrated brine stream 28 effluent may become concentratedto a level that the stream may exceed the solubility threshold withrespect to the calcium sulfate content. This calcium sulfate salt mayprecipitate on the surface of the gypsum crystals rather than on themembrane surface of the tubular membrane filter 24 and the gypsumcrystals with precipitate may be returned to the mixing tank 30. Aportion of the gypsum crystals may be removed from the system 20 asnecessary to maintain the materials balance. The gypsum crystals maytypically be at least 99.9 percent purity material that may be ofcommercial value for further use.

Referring to FIGS. 1 through 3, a reverse osmosis tubular membranefilter as understood in the industry is illustrated with the calciumsulfate process annotated. In this configuration, the concentrate brinestream 1 of the treatment process may be combined with sparingly solublesalts and introduced into a series of tubular membranes 2 under pressurethus resulting in the passage of lower salinity water 3 through themembrane surface. Elevated concentrate, sparingly soluble salts andprecipitating solids continue through the process 4 and out of theoverall membrane pressure vessel 12 for recycling. The use of the brinetreatment scaling control system 20 may result in: continuous removal ofscaling compounds from an EDR process brine loop to aid in greater EDRprocess recovery; production of scaling solids that may be in an easilydewaterable form; reduction or elimination of EDR brine process blowdownand feed water or brine stream influent make-up cycling; treatment ofhigher concentrated brine in a smaller treatment volume; reduced costsfor secondary brine treatment; reduced brine treatment chemical use; andreduced EDR process product salinity with greater salt rejection by theprocess.

While the invention has been particularly shown and described withrespect to the illustrated embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formand details may be made therein without departing from the spirit andscope of the invention.

We claim:
 1. A method for treating a brine stream comprising: treating abrine stream influent in an electrodialysis-reversal process to producea concentrated brine stream effluent and a lower salinity diluent streameffluent; processing said concentrated brine stream effluent in a brinetreatment scaling control system that has a mixing vessel and a membranefilter with said mixing vessel seeded with calcium sulfate, wherein saidprocessing produces a lowered salinity brine stream effluent and anelevated concentrated brine stream effluent; and returning said loweredsalinity brine stream effluent to a brine loop of saidelectrodialysis-reversal process wherein said electrodialysis-reversalprocess has two process flow inputs with a first input of said twoprocess flow inputs connected to a demineralization portion of amembrane stack and a second input of said two process flow inputsconnected to a concentrating portion of the membrane stack, wherein saidbrine loop is connected to said second input.
 2. The method as in claim1 wherein: said concentrated brine stream effluent is filtered in saidmembrane filter to output said lowered salinity brine stream effluentand said elevated concentrated brine stream effluent; and said elevatedconcentrated brine stream effluent is mixed in said mixing vessel toproduce a mixture that is returned to said membrane filter for furtherprocessing.
 3. The method as in claim 2 wherein a portion of saidmixture is removed at intervals necessary to maintain the materialbalance in said brine treatment scaling control system.
 4. The method asin claim 1 wherein: said concentrated brine stream effluent is routed tosaid mixing vessel to produce a mixture that is routed to said membranefilter to produce said lowered salinity brine stream effluent and saidelevated concentrated brine stream effluent wherein said elevatedconcentrated brine stream effluent is returned to said mixing vessel. 5.The method as in claim 4 wherein a portion of said elevated concentratedbrine stream effluent is removed at intervals necessary to maintain thematerials balance in said brine treatment scaling control system.
 6. Themethod as in claim 1 wherein the calcium sulfate is a gypsum crystalform of material.
 7. The method as in claim 1 wherein said membranefilter is selected from the group consisting of a nanofiltration formand a reverse osmosis form.
 8. The method as in claim 1 wherein saidmembrane filter is selected from the group consisting of ananofiltration filter, a reverse osmosis type filter, a tubular filter,a flat sheet filter, and a spiral configuration filter.
 9. The method asin claim 2 wherein a portion of said mixture is output to theenvironment.